[MITgcm-support] runoff file of cpl_aim+ocn

[Jean-Michel Campin]

Hi Fisher,

The way the "runOffMapFile" is set-up is not documented anywhere, so thanks for asking.
It contains "runOffMapSize" records of float64 (real*8) vector of length 3 each.

Each record contains a connection between a land-point from where the run-off 
 is collected and a river-mouth ocean-point where this run-off is discharged.

The 3 elements in a record are:
- first one gives the location of the Atmospheric grid-cell from where the run-off comes from. 
- second ones gives the location of the Oceanic grid-cell from where the run-off is discharged.
- third element is the catchment area (in m^2) within the atmospheric-grid cell
  that is routed to this river (cannot be larger that the atmospheric grid-cell area).

The way the location of the Atmospheric grid-cell is stored (first element) is
from the grid-cell indices (i,j) in (Nx_atm,Ny_atm) array (in cpl_aim+ocn/code_cpl/ATMSIZE.h ),
that is converted to a single integer: ijROatm = i + (j-1)*Nx_atm  
and finally converted to a real*8 (float64) value.
  
And similarly for the Oceanic grid-cell location, from its indices (i,j) in
(Nx_ocn,Ny_ocn) array (in cpl_aim+ocn/code_cpl/OCNSIZE.h ), converted to
single integer ijROocn = i + (j-1)*Nx_ocn, and then to float64.

The routine that read both this runOffMapFile is:
 pkg/atm_ocn_coupler/set_runoffmap.F
it also read-in the oceanic grid-cell area from file "RA.bin" (also float64, size
Nx_ocn x Ny_ocn), to scale the catchment area and compute the area fraction "arROmap"
that is used later in the run-off mapping (at each coupling step) in this routine:
 pkg/atm_ocn_coupler/atm_to_ocn_maprunoff.F

And I believe a partial summary of this run-off mapping is reported to the log file
of the coupler, with record number, ijROatm, ijROocn, arROmap, but only for first and
last record, as a way to check.

Cheers,
Jean-Michel

On Sun, Jan 05, 2025 at 09:38:28AM +0000, ht wrote:
> Hello,
> 
> I am currently working on a coupled simulation using the cpl_aim+ocn case from the verification directory. While modifying the bathymetry/topography files, I realized that the runOff file (default: runOff_cs32_3644.bin) also needs to be updated.
> 
> However, even after inspecting the file using MITgcmutils.utils.readbin, I couldn't fully understand the specific information it contains or the corresponding data types for each piece of information. Could you please clarify the following:
> 
> - What kind of data is stored in the runOff file?
> - What are the data types used for this information (e.g., float32, float64)?
> 
> Understanding the structure and content of the file will greatly help me make the necessary adjustments.
> 
> Thank you for your time and assistance.
> 
> Best regards,
> Fisher

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